Grokking Algorithms

What you need to know
You’ll need to know basic algebra before starting this book. In parti- 
cular, take this function: f(
x
) = 
x
× 2. What is f(5)? If you answered 10, 
you’re set.
Additionally, this chapter (and this book) will be easier to follow if 
you’re familiar with one programming language. All the examples in 
this book are in Python. If you don’t know any programming languages 
and want to learn one, choose Python—it’s great for beginners. If you 
know another language, like Ruby, you’ll be fine.

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Chapter 1
 
 
I
 
 
Introduction to algorithms
4
For example:
Here’s an example of how binary search works. I’m thinking of a 
number between 1 and 100. 
You have to try to guess my number in the fewest tries possible. With 
every guess, I’ll tell you if your guess is too low, too high, or correct.
Suppose you start guessing like this: 1, 2, 3, 4 …. Here’s how it would 
go.
Looking for companies 
in a phone book with 
binary search

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5
Binary search
This is
 simple search
(maybe 
stupid search
would be a better term). With 
each guess, you’re eliminating only one number. If my number was 99, 
it could take you 99 guesses to get there!
A better way to search
Here’s a better technique. Start with 50.
Too low, but you just eliminated 
half
the numbers! Now you know that 
1–50 are all too low. Next guess: 75. 
A bad approach to 
number guessing

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